1. Field of the Invention
The present invention relates to paper-like image recording media used in image forming devices based on electrophotography or thermal transfer and, more particularly, to reusable image recording media which are applied to an image forming device equipped also with a means for removing an image forming material such as ink from a substrate onto which the image forming material has been fixed, whereby image formation by the image forming materials and removal thereof can be repeated many times.
2. Description of Related Art
Recently, the global atmospheric problems have come to light and the importance of forest resource protection has been recognized. Reduction in utilization of wood resources as raw materials for paper has become an important problem. As one of remedies for reduction of the utilization, recycle of once used paper, without disposal as waste paper, is advanced now. Reuse of water paper is one of important means for recovering resources but has many problems, including leakage of confidential documents and/or data (particularly in companies or corporations), fractional recovery of different kinds of paper and transportation, as well as a storage space and administration of collected waste paper, in the recovery of waste paper. In the reuse of waste paper, fibers are shortened during re-pulping, leading to reduction in quality of reused paper, and an apparatus for deinking the images is further required. Since a paper-manufacturing machine is large, complex and expensive, the paper reuse can only be conducted by specific companies, not by an individual. Unless the fractional recovery, transportation, storage and operation of a huge apparatus are efficiently carried out, a large amount of energy will be consumed, i.e., the amount of CO.sub.2 discharged will be increased, whereby the warming of the earth due to increase of C.sub.2, which is also one of the global atmospheric problems, may be further accelerated.
In order to solve such a problem, there has been disclosed a method for reusing once used paper by erasing images thereon. For instance, reference may be made to the following methods.
Japanese Patent Application Laid Open (JP-A) No. 2-55195 discloses an image-erasable printing medium comprising a plastic, metal, liquid-impermeable paper or ceramic as an image support and a film of a silicone rubber releasing agent known as a silicone sealing agent coated on the surface of the support. The method for erasing an image comprises subjecting the image formed from a heat fusible ink on the support to heat and pressure through a heat fusible peeling medium followed by cooling the medium to have the image adhered to the peeling medium, thereby peeling off it from the support. The coating of the releasing agent can be migrated and partially adhered to the contract portions of, for example, a carrier roller when the agent is carried within the image forming apparatus, resulting in jamming of paper due to slipperiness. When this is repeated, the image surface may be stained since the toner floating within the apparatus may be adhered to the printed matters.
If the thickness of the coating is decreased to reduce the migration, the heat fusible ink can not be peeled out of the support. Even with regard to thinner coatings, if the surface smoothness is increased, the heat fusible ink can be peeled off. However, fixation of images decreases. In the above cited patent application publication, plain materials such as PET and laminate films having a smoothness of at least 300 seconds as measured by a Bekk smoothness tester are used as substrates. That a coating has the above-mentioned migration means that the effect of the coating as a releasing agent may be reduced upon repeated reuse. In short, the cause of migration is weak bonding such as in the case where a coating is merely applied or deposited onto a support.
On the other hand, when an image recording material is fixed on a coating having a sufficient thickness (e.g., 3 .mu.m or more) that a heat fusible ink may be peeled off, the fixation will be so poor that some fixed images may be easily peeled off only by rubbing with hands. Thus, the storage stability of recording is poor.
In short, the technique disclosed in the publication is unsatisfactory in the migration of coatings, fixation of images and peelalility.
Japanese Patent Application laid Open (JP-A) No. 5-216376 discloses a recording medium (paper) comprising a releasing agent applied on its recording surface. A toner constituting an image is transferred and removed by bringing the medium into contact, under pressure the recording paper, with a medium comprising an easily offsetting material upon erasion of the image. The releasing agent includes silicone oils, fluorinated oils and other aliphatic oils. When these oils are used, they must be applied onto a recording paper at a concentration such that the recording paper should be transparent, in order that the toner may exhibit sufficient peelability. Such a recording paper will be such a low quality that may ruin the impression of plain papers. Further, the fixation of images is also so poor that some fixed images may be easily peeled off only by rubbing with hands. Thus, the storage stability of recording is poor. Additionally, there is observed some migration resulting in the same problems as those of Japanese Patent Application Laid Open (JP-A) No. 2-55295.
Japanese Patent Application Laid Open (JP-A) No. 6-219068 discloses a reusable recording paper wherein a thermally convertible material, such as a fluorine-containing acrylate, whose adhesion with an image forming material will be lowered upon heating, is applied on or incorporated into a recording paper. (Fixation of images are conducted by pressure and the problem of the fixation with heat and pressure is explicitly mentioned.) The recording paper is for thermal transfer and has a higher smoothness than plain papers. Generally, common thermal transfer papers have a smoothness of about 200 seconds or higher as measured by a Bekk smoothness tester. Common plain papers generally have a smoothness of 20 to 100 seconds. If the smoothness exceeds 200 seconds, the impression of specialty papers increases in view of the gloss, touch and writing properties.
In order to obtain satisfactory peelability by coating or impregnating, with a fluorine-containing acrylate material, a plain paper such as a wood free paper or a copying paper having a smoothness of 160 seconds or lower, the thickness of the coating will reach 4 to 5 .mu.m and the smoothness will be 250 seconds or higher, which is within the field of specialty papers. Further, the fluorine-containing acrylate material has a bad adhesion with a thermal transfer recording paper as a substrate. Therefore it exhibits migration, so that a paper feeding roller and a recording paper may often slip in a copying machine, resulting in clogging of recording papers and/or bad printing due to misregistration. For such reasons, it is required to create a region without being coated or impregnated with the thermally convertible material on a portion of the thermal transfer recording paper; therefore it is not easy to manufacture the recording paper, resulting in a higher cost of manufacture. Further, in the electrophotographic copying machine commonly used at present, an image forming material is fixed by subjecting the recording paper to heat and pressure; therefore, the use of fixation of images with pressure only is too low in flexibility.
In the above-mentioned recording papers, the concentration of a recorded image by writing with a pencil, ball pen or aqueous pen will be low and the image is obscure, or they will repel recording materials for such writing.
In each of the above-mentioned techniques, when a color image where the whole thereof is printed in a solid form is formed by an image forming device using an electrophotographic or thermal transfer method, reproduction of the media is not easy because of poor peelability of the image thereon.